Removing silver and silver halide from photographic elements



May 29. 1956 M MADER 2,

P. REMOVING SILVER AND SILVER HALIDE FROM PHOTOGRAPHIC ELEMENTS FiledApril 1, 1954 EXPOSURE Ag G/, RED SENS/77VE CYAN COUPLE R MAGENTACOUPLER Ag 6/, GREEN 5EN5'/T/VE /NTERNAL LATENT lMAGE (Ag Br) BLUESENS/T/VE SUPPORT STAGE l GOLOR DEVELOPER OYAN DYE, Ag, Ag G/ MAGENTADYE,Ag, AgG/ LA TENT /MA6E 0F BLUE SENS/J r/0/v //v Ag Br SUPPORT lFIXING-BLEACH GYAN DYE MAGENTA DYE LATENT lMAGE 0F BLUE SENSAT/O/V /N AgBr SUPPOR T l "50/. VEN 7"0EVELOPER /2 a a 0 0 0 0 0 o a o O o cyA/v DYE/0 fSUPPORT PAUL M. MA DE R IN V EN TOR.

ATTORNEY 8 AGE T United States Patent 2,748,000 -REMOVING SILVER ANDSILVER HALIDE FROM PHOTOGRAPHIC ELEMENTS Paul M. Mader, Rochester, N.Y., assignor toEastman Kodak"Company,'Roehester, N. Y., a corporation ofApplication April 1, 1954, Serial No. 420,302 15 Claims. (Cl. 95-88)This invention relates to the removal of silver and silver 'halide fromphotographic elements. A'variety of agents for these-purposes are-knownand theselection depends on the requirements of the particular*process'involved. Thus in conventional development of asilver'halide-latent image toablack silver image it is desired to removeresidual silver halide without attacking developed silver. This can bedone with thiosulfate or thiocyanate solutions. In other instances it isdesired to remove a developed silver .imagewithout'aflectingresidualundeveloped silver halide, :for example, in "direct positivedevelopment where negative metallic silver is removed "beforeth'eresidual silver Jhalideis'developedto 'thesilverpositive image. The re-.rn'oval'is'etfectedwith 'an'oxidizingbath, such as potassiumtdichromate=sulfurie 'acide, 'or potassium "permanganate- :sulfuric acidsolution. These "bte'aches convert the silver to solublesi'lver saltswhich diffuse out of the emulsion layer, Without attacking the residualsilver :halide.

.Instillrother case'siit may-'ibe desirable ttoremove both zsilver and:silvenhalideasis truein some .color processes. "-Tlihismayzbe .done.with.a..potassium cyanide solution or with .an oxidizing .bleachsolution, .such .as idichromate,

ferricyanide, or .quinone, containing .or .followed by. a silver saltsolvent .to sensurememoval .of both the oxidized iirnage silver andlhe.residual. silver. halide.

It is diflicult to find otherwise satisfactory silver halide solvents ofsuflicient stability for use in the presence of thestrongly'oxidizing'bleach compounds. 'There are also instances where'it'is advantageous tobe able to remove the image silver along with adistinct part of the residual silver halide, for example, the silverchloride, while 'leaving comparativelyunaifec'ted anotherportion-comprising,

. for example, silver 'bromide.

.l have discovered a group of related compounds which are silver-saltsol-vents and useful for the removal of silver h'alide fromphotographi'c layers. 'Some'of them compare favorably with alkalithiosulfates and 'thiocyamates in the orthodox fixing process and inaddition have the unusual and beneficial properties of exceptional sta--bility solutions not .only to acids and --alkalies but to -.theoxidizing agents commonly used in combination :bleaching and fixingbaths for the removal of both silver and silver salts from photographiclayers. Furthermore,

1 they show ase'lectivity-"or specificityin solvent activity fordifferent silver salts commonly used in photographic layers.

These compounds are sulfur-containing diabasic acids f the-generalformula:

in which n l, 2, or 3 alkali metal or ammonium salts These compounds areuseful as fixing agents to remove silver halide from hydrophilic organiccolloid layers of photographic elements. CompoundsZ and 3 are not verysoluble in Water in'the acid form and are preferably used as .the salts,e. g.,the sodium salt. The ethylene-bis-thioglycolic acid may be usedeither in acid or salt form. It has the advantageous .property ofdissolving silver chloride at a much faster rate than it dissolvessilver bromide, so that it canbe usedfor the selectiveremoval of thechloride in thepresence of the bromide. Sodium chloride, sodium sulfite,and certain other silver halide solvents show a similar selective fixingaction, but they have one or more shortcomings which make themimpractical in many applications, e. g., slow rate of dissolving,instability in the presence of oxidizing agents, low activity, etc.

Compounds 2 and 3 are much more rapid fixing agents forsilver-halidethan ethylene-bis-thioglycolic acid. The sodium salt of Compound 2, forexample, fixes silver bromide in about one third the time required foran equimolecular concentration of ethylene-bis-thioglycolic acid. Thesodium salt of Compound 3 at 0.05 molar concentration clears a simplesilver bromide emulsion in less than half the time required for sodiumthiosulfate solution at the same molar concentration. Similarly asolution of the sodium salt of Compound 3 is a-faster acting fixingagent forsilver bromide than the sodium salt of Compound 2. A 0,05 molarsolution of the sodium salt of Compound 3 'fixed asilver bromideemulsion in one minute andforty seconds at F.

The 'Ihomologous compounds of ethylene-.bis-thioglycolic acid in whichthe ethylene .chain between the two sulfur atoms is replaced withmethylene, propylene, tetramethylene, or higher alkylene groupings formconsiderably weaker complexes than does the ethylene derivative Coni-".pound :1,: and:hence their potential value as'fixin'g agents -tdoesnot approa'hihat of 1ethylene bis-thioglycolic acid.

The exceptional stability of the fixing agents, Compounds 1, :2,and3,'becomes'apparentwhen they are used :inicombination bleaching *Jandfixing solutions for the 3removalof silverfrom'emulsions or other silvercolloid layers, such'as colloidal silver ifilter layers in photo graphic"elements. This can, of course, be "done 'by the conven- 'tional methodof firstoxidizing'th'e silver to a silver'halide 'by'itreatmentwithiferricyanide=bromide, or the like, and

' theirremoving'thesilver'halide thus'formed in a separate fixing :bath,suchas the conventionalshypo solution. it is .much more" convenient Ito"accomplish the oxidizing and bleaching operation and the solution ofthe silver salt in one step. A number of one :b'ath solutions for this:purpose are known, e. g., a reducer such as ferrocyanideilryposolutiommight vbe used. Such baths, h0W6V6l','Zli

iusuallynot suificientlystable. .My compounds enable the preparation of.a combined bleaching and fixing-solution of good stability, excellentsolvent properties for both silwer andsilverhalide, .and capable offormula and use modifications .to.permitremoval of the silver and allthe residual .silverhalide or of the silver along with selective removal.of .the .silverchloride without appreciable attack "on .the .silverbromide.

Accordingly, -aqueous .solutionscontaining a mixture of a silveroxidizing agent such as guinone or an alkali metal ferricyanide and oneof the "above sulfur-containing dibasic acids are very effective in theremoval of silver from "hydrophiliccolloidlayers of photographicelements.

Aparticul'ar application of 'one of the dibasic sulfur compounds of theinvention, ethylene-bis-thioglycolic jacid,"isin the simultaneousremoval of a silver image and silverchloridefrom "a "systemcontaining'both silver chloride "and "silver bromide as described inmore detail in the following examples. In this case it is found that a*solutionof amixture'of an oxidizing agent, e. g., quinone, andthe-dibasic sulfur'compound serves not only to dissolve the silver imagebut the ability of the ethylene-bisthioglycolic acid to selectivelyremove silver chloride from the system in the presence of silver bromideis not impaired by the presence of the oxidizing agent.

An important advantage of the mentioned bleachingfixing solutionscontaining oxidizing agent and one of the sulfur-containing dibasicacids lies in the high stability of the solutions. For example, asolution containing ethylene-bis-thioglycolic acid and quinone was foundto lose none of its power for fixing silver chloride or removing silverfrom a colloid layer after standing for eight days although the solutionhad darkened appreciably. Similarly, a solution ofethylene-bis-thioglycolic acid and potassium ferricyanide at a pH of 6.5which had been stored 50 days still fixed silver chloride and oxidizedsilver at the same rate as When the solution was first prepared. Also,the solution did not become discolored over this period of time.

The compositions of the invention containing a mixture of one of thedibasic sulfur compounds and an oxidizing agent, such asethylene-bis-thioglycolic acid and potassium ferricyanide, find use as areducer for removing metallic silver slowly from a photographic image ina manner similar to Farmers Reducer as shown in the following examples.In this case, when ferricyanide is used as the oxidizing agent, theconcentration is maintained at a low level to prevent formation ofsilver ferrocyanide in the image.

The accompanying drawings illustrate in cross-sectional view theappearance of a color film at various stages in the formation of coloredimages in the film and the selective removal of silver and silverchloride from the film in the presence of an exposed silver bromideemulsion.

My invention is described in more detail in the following examples withreference to the accompanying drawings.

EXAMPLE I A two-layer color film was prepared as described in U. S.Patent 2,490,751 and shown in Stage 1 of the accompanying drawings ashaving a support 10 carrying a gelatino silver halide emulsion layer 11containing a mixture of a green-sensitive silver chloride emulsion,magenta coupler and a blue-sensitive silver bromide emulsion of theinternal latent image type. Coated thereon is a redsensitive silverchloride emulsion layer 12 containing a cyan coupler. The film wasexposed to a colored subject and samples were processed in the followingprocesses, Process A representing a process using the conventionalbleaching and selective fixing steps and Process B incorporating thecombined fixing-bleaching step of the invention.

Process A (70 F.)

Minutes Color develop 12 Stop 1 Wash 5 Bleach Wash 5 Selective fix 9Wash 10 Develop (I) 5 Fix (I) Wash 10 Process B (70 F.)

Minutes Color develop 12 Stop 1 Wash 5 Fix-bleach 15 Wash 5 Develop (II)5 Rinse Fix (II) 3 Wash 10 The processing solutions had the followingcompositions:

Color developer:

Sodium hexametaphosphate grams 1 NazSOa (10 122-amino-5-diethylaminotoluene hydrochloride do 3 NezCOs-HzO do 20 KBr do2 H2O liter 1 Stop bath:

Acetic acid (glacial) grams 20 H2O liter 1 Bleach bath:

KzCrzOw "grams" 2 H2O liter 1 H2504 to make pH=1.9

Selective fix:

NazSOs grams H2O liter.. 1

Developer 1:

Monomethyl-p-aminophenol sulfate grams 2.2 NazSOa d0 96.0 Hydroquinonedo 8.8 NazCOs d0 48.0 KBr do... 5.0 KI do 6.0 NaOH do 10.0 H2O liter.. 1

Developer II:

Monomethyl-p-aminophenol sulfate grams.. 2.2 Na2SO3 do 96.0 Hydroquinonedo 8.8 Na2CO3 dO 48.0 KBr do 5.0 NazSzOa d0 5.0 H20 liter.. 1

Fix I:

(NH4)2S2O3 grams 250 NazSOs do 10 H2O to make 1 liter Fix II:

Water, about F. (50 C.) cc 600 Sodium thiosulfate, pentahydrate grams240.0 Sodium sulfite, desiccated do 15.0 Acetic acid, 28% cc 48.0 Boricacid, crystals grams 7.5 Potassium alum do e 15.0 Cold water to make 1.0liter Fix-bleach:

Ethylene-bis-thioglycolic acid grams 16 Quinone do 3.5 H20 liter.. 1

Accordingly, in Process A, color development forms silver and magentaand cyan dye images in layers 11 and 12 of the film, the bleach andselective fixing steps removing the silver images and residual silverchloride from the film, leaving the dye images and exposed silverbromide emulsion in the film. Subsequent development with the developerI yields a silver image of the blue sensation in layer 11. Thisdeveloper can, of course, be replaced by a solvent type of yellowimage-forming color developer such as shown in U. S. Patent 2,490,791 toyield a yellow dye image in layer 11 together with the previouslydeveloped magenta dye image and the cyan image in layer 12.

Process B embodying the combined fixing-bleaching step of the inventionis illustrated in the accompanying drawings wherein the exposed elementof Stage 1 of the drawings described above is shown in Stage 2 of thedrawings following color development, stop bath and washing steps,ascontaining magenta"an'd"cyan dye-images 'in layer 11.

Following development of the element of the third stage 'of'the drawingswith the 'black-and-white Tsolvent developer II, or a solvent typeofyellow color-forming developer, such'as shown in U. S/Patent 2,490,751,the element contains a silver, or silver and yellow dye image and themagenta dye image in layer 11 as Wellas a cyan dye image in layer .12 asdescribedin Stage 4 of .the drawings. In case a solvent type of colordeveloper has been used in the last development step, the resultantsilver image can be removed with the fixing-bleach bath of the inventionor by conventional methods, leaving only cyan, magenta and yellow dyeimages in the film.

When sensitometric curves of the subtractively colored dye images formedin the conventional Process A were compared with the curves of the dyeimages formed in Process B of the invention, it was found that thecomparable dye images of the two processes had the same contrast, andother sensitometric characteristics of the element of Process B werefavorable. In particular, the desired contrast and other characteristicswere obtained in Process B in the image corresponding to the blue lightexposure.

A fixing-bleaching bath containing about 2 to grams of potassiumferricyanide and about 16 grams of ethylenebis-thioglycolic acid perliter at a pH of about 6.5 can be used for the removal of silver imagesin processes such as that described in the above example. However, therate of removal of silver is somewhat lower than when thequinone-containing fixing-bleaching solution is used.

In those processes such as present-day color development processes, inthe final stages of which it is desired to remove silver images and allresidual silver halide in the presence of color-developed dye images,very satisfactory results will be obtained with a fixing-bleach bathcontaining an alkali salt of Compound 3 above in conjunction withferricyanide.

EXAMPLE 2 The mentioned use of the sulfur-containing dibasic acids inconjunction with an oxidizing agent as a reducer for the slow removal ofsilver from silver images in a manner similar to Formers reducer isdemonstrated by first forming a silver image in a light-sensitive filmor paper product followed by fixing in the usual manner. The film isthen treated in a solution of the following composition:

Ethylene-bis-thioglycolic acid grams 4.0 Water cc 250.0 Sodium hydroxideto bring pH to 6.5

Potassium ferricyanide grams 0.75

Treatment of a silver image developed in a high-speed negative film withthis solution at 70 C. for seconds, 1 minute, 3 minutes and 8 minutes,gave silver densities as follows:

1. Untreated image 1.85 2. 30-second treatment 1.76 3. l-minutetreatment 1.65 4. 3-minute treatment 1.42 5. 8-minute treatment 0.8

After holding the above solution for 49 days, the solution gave a silverdensity of 0.94 at Log E 3.6 when the same silver image was reduced.

The activity "of i'the reducer solution appears to be intermediate"between a proportional and a subtractive reducer solution.

"Thefollowingexampleillustrates the use of Compound '3'-for-the removalof silver-and silver halide'fromphotographic elements.

EXAMPLE 3 A multilayer .product having blue, greenand red--sensitive,gelatin emulsionlayers superposed in that order on apaperbase was provided. The emulsion layers con- .tained dispersions ofcolor-forming couplers for forming subtractively colored dye images ofcolors complementary 'to the-sensitivity of the .respective emulsionlayers. .The

..paper wasexposed in.the usual manner to a color negative and developed8 :minutes in a conventional color developing solution containingaprimary aromatic amino silver halide developing agent to obtain silverand dye images in the emulsion. layers.

After color development the .paper was treated 1 /2 .minutes with a 1aaceticacid .stop bath followed'by a 4 .minute wash and .10 .minuteswith a fix-bleach bath :0.'05 .molar insodium-3,6,9,12-tetrathiatetradecanedioate wherein n represents apositive integer of from 1 to 3 and alkali metal and ammonium saltsthereof.

2. A fixing-bleach composition for silver halide emulsion layers,comprising an aqueous solution of a mixture of quinone andethylene-bis-thioglycolic acid.

3. A fixing-bleach composition for silver halide emulsion layers,comprising an aqueous solution of a mixture of potassium ferricyanideand ethylene-bis-thioglycolic acid.

4. A fixing-bleach composition for silver halide emulsion layers,comprising an aqueous solution of a mixture of potassium ferricyanideand sodium 3,6,9,l2-tetrathiatetradecanedioate.

5. A process for the removal of silver from photographic elements whichcomprises treating a supported hydrophilic organic colloid layercontaining silver with an aqueous solution of a mixture of (1) a memberof the class consisting of quinone and an alkali metal ferricyanide, and(2) a compound having the general formula wherein n represents apositive integer of from 1 to 3 and alkali metal and ammonium saltsthereof.

6. A process for the removal of silver from photo graphic elements whichcomprises treating a supported hydrophilic organic colloid layercontaining silver with an aqueous solution of a mixture of quinone andethylenebis-thioglycolic acid.

7. A process for the removal of silver from photographic elements whichcomprises treating a supported hydrophilic organic colloid layercontaining silver with an aqueous solution of a mixture of potassiumfern'cyanide and ethylene-bis-thioglycolic acid.

8. A process for the removal of silver from photographic elements whichcomprises treating a supported hydrophilic organic colloid layercontaining silver with an aqueous solution of a mixture of potassiumferricyanide and sodium 3,6,9,l2-tetrathiatetradecanedioate.

9. A process for the selective removal of silver chloride from aphotographic emulsion layer in the presence of an emulsion layercontaining silver bromide, which comprises treating the silver chloridein the presence of the silver bromide with an aqueous solution ofethylenebis-thioglycolic acid, until the silver chloride has beenremoved leaving silver bromide in an emulsion layer.

16. A process for the removal of silver from a photographic elementcontaining a silver image, silver chloride and silver bromide whichcomprises treating said element with an aqueous solution of a mixture ofquinone and ethylene-bis-thioglycolic acid until the silver and silverchloride have been removed leaving silver bromide in the element.

11. A process for the removal of a silver image from a photographicelement containing a silver image, silver chloride and silver bromidewhich comprises treating said element with an aqueous solution of amixture of quinone and ethylene-bis-thioglycolic acid until the silverand silver chloride have been removed leaving silver bromide in theelement.

12. A process for the removal of silver halide from ahydrophilic-organic colloid photographic emulsion layer containingsilver halide which comprises treating said layer with an aqueoussolution of a compound having the general formula wherein n represents apositive integer of from 1 to 3 and alkali metal and ammonium saltsthereof.

13. A process for the removal of silver halide from a hydrophilicorganic colloid photographic emulsion layer containing silver halidewhich comprises treating said layer with an aqueous solution of sodium3,6,9-trithiahendecanedioate.

14. A process for the removal of silver halide from a hydrophilicorganic colloid photographic emulsion layer containing silver halidewhich comprises treating said layer with an aqueous solution of sodium3,6,9,l2-tetrathiatetracanedioate.

15. A process for the removal of silver chloride from a hydrophilicorganic colloid photographic emulsion layer containing silver halidewhich comprises treating said layer with an aqueous solution ofethylene-bis-thioglycolic acid.

References Cited in the file of this patent UNITED STATES PATENTS2,331,678 Hanson Oct. 12, 1943

5. A PROCESS FOR THE REMOVAL OF SILVER FROM PHOTOGRAPHIC ELEMENTS WHICHCOMPRISES TREATING A SUPPORTED HYDROPHILIC ORGANIC COLLOID LAYERCONTAINING SILVER WITH AN AQUEOUS SOLUTION OF A MIXTURE OF (1) A MEMBEROF THE CLASS CONSISTING OF QUINONE AND AN ALKALI METAL FERRICYAMIDE, AND(2) A COMPOUND HAVING THE GENERAL FORMULA